Conventionally, an engine is generally cooled by cooling water. In regard to this, Patent Documents 1 and 2 disclose arts considered as arts that are relative to the present invention as arts regarding a water jacket through which water flows. Patent Document 1 discloses a water jacket structure of an engine in which different surface properties of the water jacket formed in the engine are formed in different portions thereof. Patent Document 2 discloses a cooling structure of a cylinder liner in which a ring-shaped fin is provided to an outer circumference surface that forms a water jacket.